Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents

Definitions

• the present invention relates to a precipitant for the precipitation of phosphate ions and for the flocculation of colloids in wastewater as well as a method for producing the precipitant and its use.
• Wastewater especially municipal wastewater, contains a large part of dissolved phosphates, which lead to a strong increase in algae growth in standing or slow-flowing waters. By eliminating the dissolved phosphates, this eutrophication of the water can be prevented.
• the content of soluble phosphates in the municipal wastewater is usually in the range of the equivalent of 10 to 30 ppm of phosphorus.
• Such wastewater also contains organic colloids that can only be broken down to a small extent even with biological purification.
• phosphate removal using calcium hydroxide in the alkaline range at pH values above 9.5 is known from Klages, Meyer: GWF-Wasser, 116 (1975), pp. 370-372. It leads to low final concentrations of phosphate in the drain (below 1 ppm phosphorus), but also requires a subsequent neutralization of the wastewater, e.g. by introducing carbon dioxide.
• precipitates are obtained which are very difficult to settle and are also difficult to filter.
• the sedimented sludge must therefore be concentrated in a further stage and then usually deposited with a solids content of approx. 30%.
• the treatment of the sludge is therefore one of the most important economic factors when operating municipal sewage treatment plants.
• organic colloids by flocculation with aluminum or Can remove iron (III) salts from waste water. Such flocculation is common both in the treatment of drinking water and in the treatment of waste water.
• the solids content of the sludge formed plays an essential economic role in the process. From an economic point of view, a good precipitant or flocculant must on the one hand cause the sludge volume to be as low as possible, but on the other hand the sludge must also have a high solids content.
• iron (III) sulfate is produced from iron (III) oxide and sulfuric acid by adding a mixture of iron (III) oxide and the substoichiometric amount of sulfur. acid adds the missing amount of sulfuric acid in the form of oleum.
• the heat of dilution of the oleum serves as an energy source for the reaction. It is also necessary to pass an air stream through the reaction mixture so that the mass does not solidify into a hard block.
• the air flow is even preheated in order to be able to carry out the reaction to the end.
• separation of the iron (III) sulfate from the insoluble constituents is essential in order to obtain a usable precipitant. This process is very complex and has major corrosion problems.
• the red mud obtained in the production of aluminum oxide by the Bayer process is digested with a substoichiometric amount of sulfuric acid.
• the reaction product consists essentially of iron (III) -, aluminum sulfate and non-digested oxide residues as well as sodium sulfate.
• This process product which is relatively easy to produce, gives a precipitant which contains a considerable proportion of ineffective dietary fiber, including even soluble alkali sulfates.
• ferric oxide is reacted in aqueous suspension with a substoichiometric amount of sulfuric acid and the reaction product is then dried. Sulfuric acid is again applied to this dried material and the reaction of the sulfuric acid with the remaining iron oxide is continued with heating. Despite a reaction temperature from approx. 180 ° C only approx. 90% of the iron (III) oxide is converted to iron (III) sulfate. A complete reaction of iron (III) oxide with sulfuric acid is very difficult.
• the present invention therefore relates to a special precipitant comprising the following hydrated sulfates:
• Iron (II) sulfate 10 to 50% by weight, preferably 15 to 35% by weight, particularly preferably 20 to 33% by weight; Iron (III) sulfate, 16 to 50% by weight, preferably 18 to 40% by weight, particularly preferably 20 to 35% by weight; Aluminum sulfate, 2 to 15% by weight, preferably 3 to 12% by weight, particularly preferably 5 to 10% by weight; Magnesium sulfate, 0 to 10% by weight, preferably 3 to 10% by weight, particularly preferably 5 to 8% by weight; Titanyl sulfate, 0 to 10% by weight, preferably 3 to 10% by weight, particularly preferably 5 to 8% by weight; Water of hydration, 5 to 30% by weight, preferably 8 to 28% by weight, particularly preferably 12.5 to 25% by weight and optionally an excess of metal oxides in an amount of up to 25% by weight, based on the entire mix.
• the present invention furthermore relates to the use of the special precipitant with the composition specified above as a flocculant in water treatment and in the treatment of waste water.
• the present invention also relates to a process for producing this special precipitant and flocculant, which is characterized in that about 1 mol of iron (II) hydrogen sulfate, preferably the composition mixed with 0.6 to 1.0 mol of iron (III) oxide, which was not heated above 850 ° C during its production and the mixture is then heated to temperatures up to about 150 ° C.
• Technical iron products which, in addition to the compound FeS0 4 . H 2 SO 4 also contain other sulfates and water bound as water of crystallization.
• Technical waste products which preferably consist of Fe 2 O 3 or the oxide hydrates of trivalent iron and optionally contain iron (II) sulfate and / or iron (III) sulfate can be used as iron (III) oxide.
• Products from the roasting of technical iron (II) sulfate are particularly suitable, provided that the roasting has taken place at temperatures below 850 ° C. This is particularly well suited through the oxidative thermal treatment of FeSO 4 . 1 H 2 0 product obtained, which is often referred to in the literature as "basic iron (III) sulfate".
• the so-called filter salt which consists of approximately 50% by weight of iron (II) hydrogen sulfate, FeS0 4 . H 2 S0 4 exists, can be used in the context of the present invention as a component of the precipitant.
• a filtered sulfate mixture can have the following composition, for example:
• iron (II) hydrogen sulfate reacts with iron oxide or with the basic iron (III) sulfate, even in very small proportions, even when heat is applied externally.
• a typical hydrogen sulfate, potassium hydrogen sulfate practically does not react at all below its melting range with iron (III) oxide.
• an industrial iron hydrogen sulfate reacts with iron oxide, but only to the extent that it has not been heated above 850 ° C. or with basic iron (III) sulfate spontaneously during mixing.
• the reaction proceeds practically completely with approximately stoichiometric amounts of iron oxide or basic iron (IIIj sulfate) with heating.
• the reaction of the iron (II) hydrogen sulfate with the iron (III) oxide or the basic iron (III) sulfate can be accelerated if the reaction mixture is heated to 100 to 150 ° C. by external energy supply. Heating beyond this temperature range leads to partial dehydration of the sulfate hydrates and a reduction in the reactivity with dissolved phosphates.
• the particular advantage of this precipitant is the formation of a precipitated sludge with an unusually low sludge index, compared to the readily soluble salts of aluminum and trivalent iron that have been used as precipitants. Mixtures of readily soluble, hydrated salts, which correspond in their analytical composition to the precipitant produced according to the invention, surprisingly show a significantly higher sludge index than the precipitant.
• a mixing unit 100 kg of a sulfate mixture from the work-up of the thin acid from the titanium dioxide production were mixed with 12 kg of a roast product from the decomposition of iron (II) sulfate produced at 700 ° C. for 15 minutes.
• the sulfate mixture was an industrial iron (II) hydrogen sulfate with the following composition:
• the roasted product had the following composition:
• this re Action product is an effective precipitant for phosphate ions and a flocculant for organic colloids from aqueous solutions, for example from wastewater.
• a precipitant with the following composition was formed:
• the reaction product was a protective green, granular material with the following composition:
• the water is bound to the sulfates as crystal water. This reaction product was an effective precipitant.
• the end product has the following composition in both cases:
• the amount of sludge formed was calculated from the composition of the precipitant.
• the sludge volume index was calculated from this and from the read sludge volume.
• the sludge volume index was relatively easy to calculate even with small batches, if one calculated the precipitation product from the iron and aluminum salts for a 90% phosphate elimination and measured the sludge volume in a calibrated settling vessel.
• the precipitation product corresponds to the formula:
• the precipitated product from iron (II) sulfate corresponded to the formula given above for trivalent iron after the always occurring oxidation by the oxygen dissolved in the water.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• Separation Of Suspended Particles By Flocculating Agents (AREA)
• Removal Of Specific Substances (AREA)

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Citations (4)

• 1980
  • 1980-02-09 DE DE19803004825 patent/DE3004825A1/de not_active Withdrawn
• 1981
  • 1981-01-28 EP EP81100614A patent/EP0033903A1/de not_active Withdrawn
  • 1981-02-06 BR BR8100744A patent/BR8100744A/pt unknown
  • 1981-02-06 JP JP1585381A patent/JPS56126483A/ja active Pending

Patent Citations (4)

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